The present invention relates to a method of controlling a pump turbine which switches a runner to work as a pump and as a turbine (by changing the rotational direction of the runner).
Generally, the runner of a pump turbine, especially a high head pump turbine, is designed so as to realize a sufficient centrifugal pump action to obtain a high head during pump running.
However, this design adversely affects the turbine operation of the pump turbine. Especially when so-called S-characteristics appear as an example, it is considered to be difficult to avoid them perfectly.
It has been recognized that the S-characteristics are a bottleneck especially for high-head pump turbines in civil designing of upstream and downstream waterways, heights of installation, and so on. Therefore, there have been various proposals to control such S-characteristics. For example, Japanese Non-examined Patent Publication S53-143842 (1988) proposes a method of temporarily opening guide vanes of a pump turbine while the running point of the pump turbine is moving along a flowrate decreasing direction on the S characteristics after a load rejection and quickly closing the guide vanes when the running point of the pump turbine starts to move along a flowrate increasing direction on the S characteristics or when the flowrate becomes almost zero, as shown in the accompanying FIG. 1.
However, this proposal is designed to reduce the rotational speed (which temporarily increased after a load rejection) straight down to a predetermined rotational speed or its vicinity which is determined by a governor setting. For this purpose, the temporarily-opened guide vanes are closed as quickly as the sudden closing immediately after a load rejection instead of using the so-called buckling manner which changes the speed of closing the guide vanes from xe2x80x9climitxe2x80x9d to xe2x80x9cslowxe2x80x9d when the opening of the guide vanes Y is smaller than Ya. This is very dangerous in case the S-characteristics controller is disabled. Further this proposal assumes that the temporarily-opened guide vanes start to close when the flowrate starts to increase (from the end of decreasing) or when the flowrate becomes almost zero. However, it is very difficult to detect a flow rate finely (at high resolution) in the transient status of the pump turbine. Even if a high-resolution flowrate is detected, it is very difficult to suddenly reverse the operation of the guide vanes and it can be easily inferred that the guide vanes are opened too much. Particularly, when you keep on operating the guide vanes even after the running point on the S characteristics ends moving along the flowrate decreasing direction and starts to move along the flowrate increasing direction, the influence by the S characteristics may be greater.
Judging from the above, it can be inferred that the method in accordance with Japanese Non-examined Patent Publication S53-143842 (1988) cannot assure the steady performance in case a plurality of pump turbines share an identical penstock or particularly when the flowrate of a pump turbine changes variously not only by its own running status but also by mutual hammering by other pump turbines.
In a normal loaded operation, the pump turbine unit is linked to a huge electric power system and stability of speed control is no longer the subject to be concerned. Therefore, the governor is set in favor of response speed rather than stability. After a load rejection, however, the pump turbine must continue a no-load operation singly. Therefore, the governor is required to be set so as to assure sufficient stability in speed control.
The S-characteristics region through which the running point of the pump turbine transitionally passes has not been considered to be a condition for setting the governor gains for a no-load operation. The governor gains have been enough to assure the stability only in the first region outside the S-characteristics region in which the Q1 value decreases as the N1 value increases, but have not been sufficient to assure the stability of operation in the S-characteristics region in which a positive feedback operation works.
Switching from a setting for a loaded operation (which is in favor of higher response of the arithmetic means in the governor) to a setting for a no-load operation (which is in favor of stability) is automatically made when the actual speed is well higher than a preset speed, when a circuit breaker opens, or such conditions of load rejection occurs.
An object of the present invention is, therefore, to provide a method of controlling a pump turbine to suppress influences by water hammering due to the S-characteristics or the like and other transient phenomena and to stabilize the operations of the pump turbine.
The present invention provides a method of controlling a pump turbine to solve the above problems.
In other words, the present invention obtains the expected result by designing and/or setting the arithmetic means of a governor so that a discharge controller being closed opens temporarily at least in the leading half of the first speed decrease curve after the speed increasing upon a full load rejection (which suddenly shuts off power generated by a generator motor) turns to decrease over a first peak while the pump turbine is running in the power generation mode, to stop the first speed decrease at a point which is higher than a rated rotational speed by one third of the difference between the first speed peak and the rated speed or more, and to turn the speed to increase from the point.
In this case, the present invention controls settings of the arithmetic means of the governor to be automatically switched in order to increase the response speed before the pump turbine after a load rejection is finally settled in a no-load operation. Further the present invention automatically switches the settings of the arithmetic means of the governor when the discharge controller closes to a predetermined opening value or below after a load rejection. Furthermore the present invention automatically switches the settings of the arithmetic means of the governor when the rotational speed decreases to a predetermined value or below after a load rejection. Additionally, the present invention automatically switches the settings of the governor so that the response speed of the governor may be in the order of normal loaded operation (fastest), no-load steady state operation, and earlier stage of the first speed decrease just after a load rejection (slowest).
This switching of the settings of the governor is made without a bump. The governor is a PID governor equipped with proportion, integration, and differentiation elements and only its integral gain is switched. The governor of the pump turbine in accordance with the present invention comprises a closing speed limiter which limits the closing speed of the discharge controller according to the opening of the discharge controller. The closing speed limiter limits the closing rate of the discharge controller to a second predetermined value or less which is comparatively higher while the opening of the discharge controller is larger than a first predetermined value and to a third predetermined value or below which is comparatively lower after the opening of the discharge controller goes below the first predetermined value. The arithmetic means of the governor is controlled or adjusted so as not to start the temporary opening of the closing discharge controller until the opening of the discharge controller goes below the first predetermined value after a load rejection.
The arithmetic means of the governor is also controlled or adjusted to start the temporary opening of the discharge controller after the rotational speed increasing to the first peak upon a load rejection turns to decrease over the peak and to continue the temporary opening until the speed reaches an inflection point at which the rotational speed curve turns from a convex curve to a concave curve. The arithmetic means of the governor is also controlled or adjusted to start the temporary opening of the discharge controller a little earlier than a time point at which the speed increase just after load rejection stops.
Further, the arithmetic means of the governor is also controlled or adjusted to start the temporary opening of the discharge controller a little earlier than a time point at which the speed increase just after load rejection stops and to continue the temporary opening until the speed reaches an inflection point at which the rotational speed curve turns from a convex curve to a concave curve. The arithmetic means of the governor is also controlled or adjusted to automatically change the gain settings of the governor from the response speed priority setting for a loaded operation to the stability priority setting (suitable for suppressing the adverse influence of S-characteristics) when the rotational speed exceeds a predetermined value higher than a rated rotational speed.
The present invention relates a pump turbine comprising a governor which monitors the rotational speed of the runner and controls the discharge controller to settle the speed of the runner steadily to a predetermined value. The arithmetic means of said governor is controlled and set (which is called S-characteristics setting) to temporarily open the closing discharge controller just before a first peak of the speed curve at which the speed increasing upon a full load rejection turns to decrease over the peak or in the leading half of the first speed decrease curve upon a full load rejection (which shuts off power generated by a generator motor) and to make a time period between the first peak and a speed value equal to the sum of the rated speed and a speed deviation according to the speed droop setting twice as much as or more than a time period between the start of the first speed rise and the first peak.
If in the Power Generation mode a load rejection or emergency stop accompanied by a speed rise occurs, the governor controls to quickly closes the discharge controller immediately after the speed starts to increase, but the governor controls to turn the closing discharge controller to open in the leading half of the speed rise, to continue opening the discharge controller approximately until the speed reaches the peak, to stop the discharge controller to open there, then to turn the discharge controller to close.
If in the Power Generation mode a load rejection or emergency stop accompanied by a speed rise occurs, the governor controls to quickly closes the discharge controller immediately after the speed starts to increase, but the governor controls to gradually decrease the closing rate of the discharge controller, turn the discharge controller to open smoothly in the leading half of the speed rise, to continue opening the discharge controller approximately until the speed reaches the peak, to gradually decrease the opening rate of the discharge controller, then to smoothly turn the discharge controller to close again.
If in the Power Generation mode a load rejection or emergency stop accompanied by a speed rise occurs, the governor controls to quickly closes the discharge controller immediately after the speed starts to increase, but the governor controls to turn the closing discharge controller to open in the leading half of the speed rise, to continue opening the discharge controller approximately until the speed reaches the peak, to stop the discharge controller to open there, then to turn the discharge controller to close.
Consequently, upon a full load rejection or almost full load rejection, the governor controls to make a time period between the occurrence of a load rejection and the reach of the speed to the first peak 1.5 times or above a time period between the first peak and the reach of the speed to the sum of the initial speed before the load rejection plus one third of the difference between the first peak and the initial speed before the load rejection.
If in the Power Generation mode a load rejection or emergency stop accompanied by a speed rise occurs, the governor controls to quickly close the discharge controller immediately after the speed starts to increase, but the governor controls to gradually reduce the closing rate of the discharge controller in the leading half of the speed rise, to smoothly turn the discharge controller to open, to continue opening the discharge controller approximately until the speed reaches the peak, to gradually reduce the opening rate of the discharge controller, and to smoothly turn the discharge controller to close. Consequently, upon a full load rejection or almost full load rejection, the governor controls to make a time period between the occurrence of a load rejection and the reach of the speed to the first peak 1.5 times or above a time period between the first peak and the reach of the speed to the sum of the initial speed before the load rejection plus one third of the difference between the first peak and the initial speed before the load rejection.
If in the Power Generation mode a load rejection or emergency stop accompanied by a speed rise occurs, the governor controls to quickly close the discharge controller immediately after the speed starts to increase, but the governor controls to turn the closing discharge controller to open in the leading half of the speed rise. Consequently, upon a full load rejection or almost full load rejection, the governor controls to make a time period between the occurrence of a load rejection and the reach of the speed to the first peak 1.5 times or above a time period between the first peak and the reach of the speed to the sum of the initial speed before the load rejection plus one third of the difference between the first peak and the initial speed before the load rejection.
If in the Power Generation mode a load rejection or emergency stop accompanied by a speed rise occurs, the governor controls to quickly close the discharge controller immediately after the speed starts to increase, but the governor controls to turn the closing discharge controller to open in the leading half of the speed rise, to continue opening the discharge controller until the speed reaches the peak, to stop opening the discharge controller, and to turn the discharge controller to close
While the speed is increasing after a load rejection, the closing discharge controller can be turned to open by temporarily adjusting or switching the settings of the governor.
Its embodiment is to correction-control the governor so that the target speed of the runner may be temporarily higher immediately after a load rejection or an emergency stop command is made.
Or another embodiment is to correction-control the governor so that the target speed of the runner only in the transient status immediately after a load rejection may be substantially higher than the target value in the steady status.
Further, the present invention is characterized by correction-controlling the governor to substantially increase the target speed as the speed increases immediately after a load rejection gradually releasing (or decreasing) the correction control after the speed turns to go down, and releasing the correction-control substantially completely in the steady status.
The present invention is also characterized by changing from fast closing of the discharge controller smoothly to the above-mentioned opening so that the upstream penstock water pressure which increased during fast closing of the discharge controller immediately after a load rejection may be consequently retained at an approximately identical value until the speed reached the peak.
The governor is a PID governor equipped with proportion, integration, and differentiation elements. The operation to cause the closing discharge controller to turn to open while the speed is increasing after a load rejection is realized by temporarily reducing the gain of the proportion element, the gain of the integration element, or both.
Further, the operation to cause the closing discharge controller to turn to open while the speed is increasing after a load rejection is realized by automatically switching the settings of the governor so that the response speed of the governor may be in the order of normal loaded operation, no-load steady operation, and the first speed increasing stage just after a load rejection.
Further, the arithmetic means of the governor is automatically switched from a response priority setting for a loaded operation to a stability priority setting when the speed exceeds a predetermined value which is higher than the rated speed.
Furthermore, the setting of the arithmetic means of the governor is automatically switched from a setting for the above temporary opening operation to a setting for a no-load operation thereafter when the discharge controller is closed to a predetermined opening or below or when the speed goes below a predetermined value.
The governor controls to cause the discharge controller to temporarily open in the Power Generation mode and upon a load rejection which shuts off power generated by the generator motor.
In the Power Generation mode and upon a load rejection which shuts off power generated by the generator motor, the discharge controller is temporarily opened at least once before decreasing of the speed of the runner is accelerated too much after the peak.
A correction signal generator is also provided to supply correction values to the governor to correct the output signal of the governor. Upon a load rejection, the correction signal generator outputs a correction value to make the rate of decrease of the rotational speed of the runner much slower than the rate of increase of the rotational speed.
A correction signal generator is also provided to supply correction values to the governor to correct the output signal of the governor. The correction signal generator corrects signals of the governor to eliminate the second water hammering peak in the upstream side of the turbine which occurs immediately after the rotational speed of the runner starts to decrease after a load rejection which shuts off the generator motor from the power generation system.
A correction signal generator is also provided to supply correction values to the governor to correct the output signal of the governor. The correction signal generator corrects the output signals of the governor to eliminate the second water hammering peak in the upstream side of the turbine which occurs immediately after the rotational speed of the runner starts to decrease after a load rejection which shuts off the generator motor from the power generation system.
The discharge controller is temporarily opened by switching, changing, or modifying the transfer function of the arithmetic means of the governor after a load rejection or in the transient status after a load rejection.
Further, the present invention is provided with an opening limiter of the discharge controller which may be closed according to a predetermined program after a load rejection or in the transient status after a load rejection so that the opening of the discharge controller opened temporarily is limited and closing of the discharge controller thereafter is assured.